Antennas



1959 D. E. R. LANDER ,87 ,4

ANTENNAS Filed May 16. 1955 D. 5 1?. lam DEA? B14 y, y w

2,871,478 ANTENNAS Denis Evald Reinhold Lander, Sunne, Sweden Application May 16, 1955, Serial No. 508,588 Claims priority, application Sweden May 22, 1954 10 Claims. (Cl. 343857) The present invention relates to antennas, and more particularly to antennas for high frequency radiation, and especially for receiving television signals.

The invention has for its object to provide an antenna structure possessing, inter alia, the following advantages over antennas as hitherto known:

(l) The antenna is readily adaptable to different frequency bands within the ultra high frequency range without necessitating any replacement of elements.

(2) The antenna is adjustable so as to enable comparatively wide frequency bands to be received.

(3) The antenna is variable and may easily be matched to the characteristic of an existing feed line in order to avoid reflections.

(4) The antenna is susceptible of being designed in a manner also to warrant good reception within the usual long and intermediate wavelength broadcast bands.

According to the present invention, an antenna of the class indicated is characterized mainly therein that it comprises a conductor which is helically shaped and which has connected at various points a number of pairs of antenna rods, the two rods of each such pair forming with the intervening portion of said helical conductor a circuit which is tuned for the reception of the frequency of the desired wave, or to a frequency in the vicinity thereof, a feed line being connected across a portion of the part of said helical conductor which is disposed between two pairs of rods.

The invention will now be described with reference to the accompanying drawing which illustrates, by way of example, an antenna array according to a preferred form of the invention.

Fig. l is a side view of the antenna array.

Fig. 2 shows a top extension member.

Referring to the drawing, numeral 1 designates a supporting rod, preferably made of metal. This rod has two cup-shaped insulating members 3 and 5 attached to it in longitudinally spaced relation. Disposed around the central rod 1 between these insulators 3 and 5 and attached to the same is a helically shaped conductor 2 which, in the embodiment illustrated, is formed by a length of metal strip wound edgewise.

At various points of the helical conductor 2 four rodshaped antenna elements 6a, 6b, 6c and 6d are connected thereto in such a manner as to interpose between the rod 6a and the rod 6b a number of N turns of the helical conductor, between the rod 60 and the rod 60 a number of N turns thereof, and between the rod 61) and the rod 6c a number of N turns of the same.

The antenna rods 6a to 6d are releasably connected by suitable contact clips to the helical conductor 2 so as to enable their points of attachment to be altered. The antenna rods are carried by U-shaped brackets 12 made of any suitable insulating material. The open ends of the legs of each bracket 12 are attached to the central rod 1 by screw clamps whereby, after releasing these screw clamps, the bracket can be disengaged from the rod 1 and be moved to a different point along the rod, as desired, and be reattached to the rod at the latter point by tightening its screw clamps again.

As will be apparent from the drawing, each one of the antenna rods 6a to 6d, is composed of two or more parts associated with one another in a telescopic fashion so as to enable each antenna rod to be extended or shortened, as desired.

It is not essential, however, to make the antenna rods as telescopic members, although this may be of advantage from the point of view of tuning. Where they'are in the form of telescopicmembers, they should be made of a very thin-gage material.

The rods 6a and 6b together with the turns N of the helical conductor disposed between these rods form a resonant circuit which will hereinafter be denoted by A, and the resonance frequency of which depends on the effective lengths of the antenna rods 6a and 6b as well as of the number of turns N of the helical conductor 2. In this similar manner, the rods 6c and 6d form together with the turns N of the helical conductor another resonant circuit designated hereinafter by B. The resonant frequency of this circuit is dependent of the lengths of the rods 6c and 6d and of the number of turns N Situated between the two rods 6b and 6c are a number of turns N of the conductor 2. This portion of the conductor 2 together with the members connected thereto forms a further resonant circuit denoted hereinafter by C.

The circuits A and B may be tuned to identical resonant frequencies, but they may also be tuned to frequencies differing from each other by a few megacycles per second. In the latter case the antenna will display more pro nounccd wide band characteristics than in the former case. The circuit C may also be tuned to the same frequency as the circuits A and B, or its resonant frequency may differ therefrom, according to the characteristics required from the antenna.

As illustrated in the drawing, a feed line 11 is connected across some of the turns N forming the resonant circuit C. The points of connections of the feed line at these turns may be changed, and by altering the points of connection of the feeder wires so as to include a greater or smaller number of the turns N it is possible to match the impedance of the antenna (as seen from the feeder) so as accurately to correspond to that of the feeder. An extremely satisfactory impedance matching has been found to be obtainable in this way and to be substantially independent of the range of wavelengths within which the I antenna is designated for optimum operation. It is "possible by this impedance matching to obtain in the feed line a standing-wave ratio better than 1.1.

The conductor turns N may be considered as the primary winding of a matching transformer the secondary winding of which consists of the number of turns included between the feeder wires.

Although the helical conductor 2 has been illustrated as consisting of a metal strip wound edgewise, other constructional forms are conceivable within the scope of the present invention. Thus, the conductor may be formed by a helically wound wire, or by a tubular member bent into helical shape. However, a strip member wound edgewise has been found to involve certain advantages as compared to a wire or tube. In the first place, a very satisfactory mechanical stability will be obtained, and in the second place the turns of the strip member will form a relatively low capacitance with the central supporting rod which involves a lower parallel capacitance of the coil formed by the conductor 2 as a whole. Further, the strip has a great outer surface area which involves decreased'resistance losses at the high frequencies involved in this field of application.

As already pointed out, the antenna of the invention, operates within a frequency range which is very wide as compared to previously known antenna structures. This seems to be due to the fact that the helical conductor 2 with the antenna rods and coupling members connected thereto form together with their stray capacitances a great number of parallel and series resonant circuits. The capacity of receiving a wide band of frequencies is of great importance in connection with television reception.

Practical tests have shown that it is possible, with an antenna according to the invention, to attain good television reception conditions on all television channels allotted to Sweden, and, in addition, to attain very satisfactory broadcast reception within the ultra high frequency, intermediate frequency and longwave ranges without the necessity of making any alterations to the antenna.

According to one embodiment of'the present invention, the supporting rod or mast 1 may be insulated base, such as a. roof or the like, on which it: is mounted, and provided with a separate down lead. The rod 1 then forms a separate antenna serving for reception at the common broadcast frequencies. The rod ll may be pro vided with a top extension member 4 which may be extensible for increasing the height of the antenna. The extension member 4, alternatively, may be insulated from the rod 1 and serve alone as a receiving antenna for the common broadcast'bands.

In one embodiment of the present invention the rod 1 and/or its extension member 4 serves as a dipole for vertically polarized short waves. reception is obtained also of a horizontal comp nent of the vertically polarized wave. It has been found possible to receive a vertically polarized Wave even though the rod 1 and/or its. extensionmcmber are not tuned to the frequency of the wave received, particularly if cerconductor 2, are tuned to sp te of the tain of the circuits formed by the helical such as, for example, the circuits A and B, the frequency of the wave received, for in antenna showing a very good wide-band efiiciency it is possible, of course, to adjust the same in a manner to favor the reception of a particular short-wave channel.

A coaxial cable, the upper end of which is shown at 10, may be connected to the helical conductor 2 to serve as a down lead when the said conductor is to be used as an antenna. The cable may also be connected to the sup- 1 portingrod 1 and/ or to the top-extension 4 if it is desired to use the one or other of these elements as an antenna. In a manner previously known per se this down lead may be combined with the: down lead 11 connected to the other section of the antenna structure.

It may be advantageous to connect the rod 1 to ground. Thereby an eflicient lightning protection will be obtained. The lightning protection will. be very efiective in the case where the rod 1 has an extension 4 electrically connected with the rod 1. However, even if the extension 4 is insulated from the rod 1a good lightning protection is obtainable by arranging a suitable spark gap betweenthe rod 1 and its-extension 4.

Owing to the structuralarrangement of the antenna its mode of utilization maybe varied in many ways. Thus, for-instance, theantenna rods 6 may be adjusted so as toinclude an; angle: between them whereby a V-shaped antenna will be obtained. Also, the antenna rods may be bentror. otherwise suitably shaped so as directly to adapt theantenna-for the reception of a vertically polarized wave.

Although the invention has been described hereinabove in conjunction with a specific, preferred embodiment thereof, it-should be understood. that several modified tions are conceivable without departing from its scope. Thus it is possible to connect two or. more helical condoctors-with antenna rods similar to the structure shown on the drawing in parallel to a commonfeed line 11, the

two structures being preferably carried one above the other by a single central rod 1.

. What I claim is:

1. An antenna for the reception of high and ultra high frequency radiation including television signals, com prising a helically wound conductor, pairs ofantenna rods connected to said helical conductor at various points thereof, the two rodsof each pair extending radially in diffrom the With this arrangement ferent directions from said conductorand torming'with the intervening portion. thereof. azresonant circuit tuned for the reception of the frequency of a11desired wave,. and

a helical conductorconsists of a metal strip wound edgewise.

3. An antenna as claimed in claim 1, wherein said antenna rods are telescopically extensible.

4. An antenna as claimed in claim I, wherein said antenna rods are releasably connected by contact clips to the helical conductor so as to enable their points of at; tachment to be altered.

5. An antenna for the, reception of high and ultra high frequency radiation including television signals, comprise ing a helically wound conductor, pairs of antenna rods connected to saidhelical conductor at various points thereof, the two rods of each pair extending radially in different directions from said conductor and forming with the intervening portion thereof a resonant circuit tuned for the reception of the frequency of a desired wave, a feed line connected across a portion of the part of the helical conductor disposed between two pairs of antenna rods, said portion being such that the impedance of the antenna. as seen from the feedline substantially equals the impedance of said feed line, a rod disposed centrally within said helical. conductor, and insulating members carried by said central rod and serving to support said helical conductor, said central rod having such dimensions and electrical'conductivity as to reduce considerably the ratio between the reactive impedance and the resistance of the helical conductor.

6. An antenna as claimed in claim 5, wherein each of said antenna rods is carried by a U-shaped bracket at tached to said central. rod through the medium of screw clamps so as to be swingableand slidable thereon.

7. An antenna for the reception of high and ultra high frequency radiation including television signals, comprising a helically Wound conductor, pairs of antenna rods connected to said helical conductor at various points thereof, the two rods of each pair extending radially in different directions from said conductor'j and forming with the intervening portion thereof a resonant circuit tuned for the reception of the frequency of a desired wave, a feed line connected across a portion of the part of the helical conductor disposed between'two pairs of antenna rods, said portion being such that the impedance of the antenna as seen from the feed line substantially equals the impedance of said feed line, a rod disposed centrally within said helical conductor, insulating members carried by said central rod and serving to support said helical condoctor, said central rod having such dimensions and electrical conductivity as to reduce considerably the ratio between the reactive impedance and the resistance of the helical conductor, and an extension provided at the top of said central rod and arranged to serve as an antenna for the reception of normal broadcast wavelengths.

8. An antenna as claimed in claim 7, wherein said extension is telesco'ucally extensible.

9. An antenna as claimed in claim 7,- wherein said extension is insnlated from said central rod.

10. An antenna as claimed in claim 7, wherein a separate feed lead in the form of a coaxial cable is con-- nected to the said supporting rod and the extension there of.

' References Cited in the: file-of this patent UNITED STATES PATENTS 218,708 

